1. Field of the Invention:
The present invention comes within the technical sphere of renal insufficiency and relates to replacement equipment used for the extracorporeal filtration of the blood in the case of acute temporary deficiencies or chronic deficiencies.
2. Description of the Prior Art:
There are many prior art practices for performing this replacement function.
A first method uses an exchanger, which is an apparatus divided into two compartments by a semi-permeable membrane. One of the compartments is connected to the patient by extracorporeal blood circulation lines, and the second compartment is connected to a circulation line for the ultrafiltrate extracted from the blood which is collected in a collecting bag provided for this purpose.
An installation of this type can cause spontaneous or assisted blood circulation to take place. The operating principle of such an installation is based on a convection phenomenon employing differential pressures to allow excess water to be extracted and eliminated from the blood.
This method is known as continuous ultrafiltration. It is particularly suitable for a rapid elimination of excess water and simultaneously allows a limited elimination of the metabolic waste products drained by the extracted ultrafiltrate.
Such a method is particularly suitable for the treatment of acute cases where the primary concern is to restore the patient to an acceptable weight by the elimination of excess water.
Such a method is, on the other hand, not suitably adapted to the elimination of the metabolic waste products. The purification of the blood is, in fact, limited by the quantity of ultrafiltrate which can be extracted from the blood.
Another practice, which is termed continuous haemofiltration, uses an installation identical to that described above which is, however, completed by the connection of a spontaneous or assisted line infusing a physiologically sterile, pyrogen free solution into the extracorporeal blood circulation line which is thereby added to the blood to offset the quantity of ultrafiltrate extracted, except for the loss of weight.
Again, this practice employs the convection phenomenon to cause a pressure differential, but the supply of the physiological solution makes it possible to obtain a substantially greater extraction of the metabolic waste products by making provision for longer treatment times.
It will be understood that, because of the infusion of a physiological solution, such a method may not be appropriate in the initial treatment stage in some acute cases where the priority object is a rapid restoration of the patient's normal weight. This is the reason why, in practice, such a method is frequently substituted for the first method after the latter has made it possible to achieve the priority object, and it is then necessary to ensure that the elimination of the metabolic waste products is really obtained.
A third method, known as continuous haemodialysis, is performed by connecting the inlet of the second compartment of the exchanger of the installation to a reservoir for a physiological solution which is caused to circulate in the second compartment, generally in contraflow with the blood circulation, while maintaining the pressure relationship and flow rate relationship with respect to the blood circulation conditions.
The main flow rate relationship is established to create conditions for diffusion through the semi-permeable membrane in the blood compartment-physiological liquid compartment direction. Moreover, the effect of the pressure relationship is to create a transfer by convection from the blood compartment toward the physiological liquid compartment. By this means, it becomes possible to improve the extraction of the metabolic waste products by means of the circulation of the physiological liquid, and more particularly the elimination of small molecules, such as urea.
This method also has a potential for more effective treatment, because it allows better purification of the blood according to commonly accepted criteria.
It may be seen, therefore, that the three known methods per se have, in the sequence in which they are discussed above, a decreasing efficiency for eliminating excess water and increasing efficiency for elimination of the metabolic waste products.
Clinically, it is frequently found that in acute cases the trends in the behavior of the deficient organism require recourse to a treatment method different from the one being applied.
Thus, after a stage of treatment by a continuous ultrafiltration method with a view to restoring normal weight, recourse is frequently made to the continuous haemodialysis. However, with the application of one or the other of the methods, one can sometimes find a fresh solution of water which again has to be rapidly eliminated by recourse to the first method.
Moreover, during a stage of treatment by continuous haemofiltration, it is possible to find modifications of the patient's catabolism, requiring a more effective purification of the blood which, in certain cases, can only be effected by application of the continuous haemodialysis method.
The practitioners are therefore confronted with the problem of frequent change from one installation to another to meet developments in a particular clinical case during the course of treatment.
At the present time, recourse to one or the other of the methods necessarily entails the use of an installation which is appropriate to the method in question and setting up each time the connection of such an installation in communication with the patient to be treated by the appropriate practice. This is not satisfactory, because it represents a considerable constraint for the staff charged with the follow-up of the clinical case to be treated, a significant source of errors with respect to the connections and/or of the relationships of the pressure and flow rates, and requires that a considerable number of installations be provided in reserve. These reserve installations are required because each installation once having been used as a specific connection cannot be modified without incurring the risk of infection.
Thus, there is a need for an installation that allows the practitioner to have the capability for applying one of the three methods in the course of treatment, with the option of changing to another if the priority objective is loss of weight rather than an average or high elimination of the waste products, or vice versa.